Apparatus and method for transmitting/receiving data in a multi-antenna system, and system using the same

ABSTRACT

A data reception apparatus and method for generating and transmitting feedback information in a multi-antenna system using grouped antennas, and a data transmission apparatus and method for transmitting a data stream of a user according to a transmission mode selected depending on the feedback information is disclosed. The reception apparatus generates feedback information depending on maximum channel quality information, an antenna group index associated with the maximum channel quality information, rank information, and remaining channel quality information associated with the rank information, and transmits the feedback information to the transmission apparatus. The transmission apparatus selects one of a multi-user mode and a single-user mode as a transmission mode depending on the feedback information and transmits a data stream of a user via multiple antenna groups or one antenna group, according to the selected transmission mode.

PRIORITY

This application is a Continuation of U.S. patent application Ser. No.11/896,479, which claims priority under 35 U.S.C. §119(e) of U.S. PatentProvisional Application No. 60/841,246, filed Aug. 31, 2006, in theUnited States Patent and Trademark Office, and claims the benefit under35 U.S.C. §119(a) of Korean Patent Application No. 2007-73155, filedJul. 20, 2007, in the Korean Intellectual Property Office, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a data transmission/receptionapparatus and method in a multi-antenna system, and a system using thesame. More particularly, the present invention relates to an apparatusand method for transmitting/receiving data by antenna grouping, and asystem using the same.

2. Description of the Related Art

Conventionally, the wireless channel environment, unlike the wiredchannel environment, shows a lower reliability due to multipathinterference, shadowing, propagation loss, time-varying noise,interference, etc. This is the typical cause of obstruction to anincrease in a data transfer rate, or a data rate, in mobilecommunication. Therefore, to implement a high-speed wireless environmentfor providing high-rate services, there is an urgent need for a solutionto the foregoing problem.

A Multi Input Multi Output (MIMO) multi-antenna system is a conventionaltechnology that has been proposed for addressing the problem of lowerreliability in a wireless channel environment. The proposed MIMOmulti-antenna system has an advantage of being capable of increasingperformance of the system without addition of power and spectrum.

Generally, the multi-antenna system supports a Single-User (SU) mode anda Multi-User (MU) mode. A multi-antenna system supporting the SU modetransmits data to the same user via multiple transmission antennas, anda multi-antenna system supporting the MU mode transmits data to multipleusers via multiple transmission antennas. The multi-antenna systemsupporting the MU mode has been proposed to obtain improved performancecompared to the multi-antenna system supporting the SU mode, whileminimizing an increase in the number of antennas and an increase incomplexity of the hardware structure. In addition, the MU mode laysemphasis on improvement of the system's transmission capacity usingSpatial Division Multiple Access (SDMA) scheduling.

The multi-antenna system is classified into a closed-loop scheme thatdepends on feedback information for resource allocation, and aclosed-loop that does not depend on feedback information. For theclosed-loop scheme, the most important issue is to prepare a scheme forminimizing feedback information for efficient resource allocation.Particularly, in the MU mode, there has long been a need for a reductionin the amount of feedback information.

Meanwhile, due to the diversification of the wireless communicationservices, there is a probability that terminals having differentcharacteristics will coexist in the same service area. Therefore, a basestation should be able to support various communication schemes. Forexample, the base station should be able to selectively support not onlythe SU mode but also the MU mode. In addition, for signal detection, thebase station should be able to support both a terminal using a lineardetection technique and a terminal using a nonlinear detectiontechnique.

Accordingly, there is a need for an improved apparatus and method forgenerating and transmitting feedback information in a multi-antennasystem using grouped antennas, and a data transmission apparatus andmethod for transmitting a data stream of a user according to atransmission mode selected depending on the feedback information.

SUMMARY OF THE INVENTION

In accordance with an aspect, a method for receiving/transmitting datain a closed-loop multi-antenna system defines multiple antenna groups byantenna grouping on multiple antennas, and performs data transmissionindividually via each of the multiple antenna groups. The methodincludes receiving, by a transmitter, feedback information from at leastone receiver, and calculating, by the transmitter, each of a sum rate(R_MU) in a multi-user mode and a sum rate (R_SU) in a single-user modeusing the feedback information. The method also includes selecting, bythe transmitter, one of the single-user mode and the multi-user mode asa transmission mode using a comparison result between the sum rate(R_MU) in the multi-user mode and the sum rate (R_SU) in the single-usermode, and transmitting, by the transmitter, a data stream according tothe selected transmission mode. The method also includes, acquiring, bythe at least one receiver, channel quality information (CQI) for eachdata stream transmitted individually via each antenna groupcorresponding to the transmission mode. The method includes determining,by the at least one receiver, CQI associated information from the CQIacquired individually for each antenna group, and transmitting, by theat least one receiver, the determined CQI associated information to thetransmitter as the feedback information. The CQI associated informationincludes maximum CQI, an antenna group index associated with the maximumCQI, rank information, and remaining CQI associated the rankinformation.

In accordance with another aspect, a closed-loop multi-antenna systemdefines multiple antenna groups by antenna grouping on multipleantennas, and performs data transmission individually via each of themultiple antenna groups. The closed-loop multi-antenna system includes atransmitter including a feedback information processor and a firsttransmit unit, and at least one receiver including a channel estimator,a feedback information generator and a second transmit unit. Thefeedback information processor for receiving feedback information fromthe at least one receiver, calculating each of a sum rate (R_MU) in amulti-user mode and a sum rate (R_SU) in a single-user mode using thefeedback information, and selecting one of the single-user mode and themulti-user mode as a transmission mode depending on a comparison resultbetween the sum rate (R_MU) in the multi-user mode and the sum rate(R_SU) in the single-user mode. The first transmit unit for transmittinga data stream according to the selected transmission mode. The channelestimator for acquiring, CQI for each data stream transmittedindividually via each antenna group. The feedback information generatorfor determining, CQI associated information from the CQI acquiredindividually for each antenna group corresponding to the transmissionmode, and the second transmit unit for transmitting the feedbackinformation to the transmitter. The CQI associated information includesmaximum CQI, an antenna group index associated with the maximum CQI,rank information, and remaining CQI associated the rank information.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certainembodiments of the present invention will become more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a closed-loop multi-antenna systemaccording to an embodiment of the present invention;

FIG. 2 is a diagram illustrating an example of a detailed structure of areception apparatus according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating an exemplary operation of a receptionapparatus for generating feedback information according to an embodimentof the present invention;

FIG. 4 is a diagram illustrating an operation performed in a receptionapparatus with, for example, two antenna groups according to anembodiment of the present invention;

FIG. 5 is a diagram illustrating an example of a detailed structure of atransmission apparatus according to an embodiment of the presentinvention; and

FIG. 6 is a diagram illustrating a control flow performed in atransmission apparatus according to an embodiment of the presentinvention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention and are merely exemplary. Accordingly,those of ordinary skill in the art will recognize that various changesand modifications of the embodiments described herein can be madewithout departing from the scope and spirit of the invention. Also,descriptions of well-known functions and constructions are omitted forclarity and conciseness.

Preferred embodiments of the present invention will now be described indetail with reference to the annexed drawings.

A reception apparatus proposed by an exemplary embodiment of the presentinvention, described below, generates feedback information including thebest channel quality information out of channel quality informationassociated with each data stream group, an index of a data stream groupassociated with the best channel quality information, the number (orRANK value) of activated transmission stream groups, which isinformation additionally needed for a flexible SU mode, and channelquality information based on the number (RANK value) of activatedtransmission stream groups. The index of the data stream group isinformation necessary during base station scheduling for supporting theMU mode. The flexible SU mode can be defined including both atransmission mode for transmitting a data stream associated with oneuser via one antenna group and a transmission mode for transmitting thedata stream via multiple antenna groups. Therefore, in an exemplaryembodiment of the present invention described below, the SU mode shouldbe construed as the above-defined flexible SU mode.

It can be assumed that for generation of a channel quality value for theMU mode and generation of a channel quality value for the flexible SUmode, the reception apparatus can use either the same receiver ordifferent receivers according to its own conditions. For example, it canbe assumed that the reception apparatus can use a linear receiver forgeneration of a channel quality value for the MU mode, and a nonlinearreceiver, such as Successive Interference Cancellation (SIC) receiverand Modified Maximum Likelihood (ML) receiver, for generation of achannel quality value for the flexible SU mode.

A detailed description will be made herein of a multi-antenna systemsupporting both the SU mode and the MU mode based on antenna grouping.Further, a detailed description will be made of a structure andoperation of a reception apparatus for generating and transmittingfeedback information according to a data stream transmitted by means ofantenna grouping, and a detailed description will also be made of astructure and operation of a transmission apparatus for transmitting adata stream via an antenna group grouped by means of a transmission modedetermined based on the feedback information.

A. Multi-Antenna System

FIG. 1 illustrates a closed-loop multi-antenna system according to anexemplary embodiment of the present invention. The multi-antenna systemshown in FIG. 1 includes one transmission apparatus 110 and multiplereception apparatuses 120-1 and 120-N. The transmission apparatus 110can be assumed to be a base station, and the multiple receptionapparatuses 120-1 and 120-N each can be assumed to be user terminals.The following description will be made with reference to one receptionapparatus 120-1, and the same can be applied to the other receptionapparatuses.

Referring to FIG. 1, the transmission apparatus 110 includes N_(t)antennas, and the reception apparatus 120-1 includes N_(r) antennas. TheN_(t) antennas included in the transmission apparatus 110 are grouped bya predetermined number of antennas. This is called ‘antenna grouping’,and an antenna bundle obtained by the grouping is called an ‘antennagroup’. However, a multi-antenna system using a precoding matrix canapply grouping for columns, and grouping for beams. In this case, thepresent invention can be implemented by means of “column group” or “beamgroup” rather than the “antenna group”. Therefore, the “antenna group”as used herein should be construed to include the “column group” and the“beam group”. For convenience, the number of antenna groups herein isassumed to be 2. Therefore, each antenna group is composed of N_(t)/2antennas.

The transmission apparatus 110 transmits a data stream for each user viaan antenna group based on feedback information provided from thereception apparatus 120-1. That is, the transmission apparatus 110determines a transmission mode for transmitting the data streamdepending on the feedback information. The transmission mode isclassified into the SU mode and the MU mode. The SU mode is divided intotwo transmission modes depending on rank information. In addition, thetransmission apparatus 110 determines a Modulation & Coding Selection(MCS) level depending on the feedback information. The data streamstransmitted via multiple antennas constituting the antenna group will bereferred to herein as a ‘data stream group’.

The reception apparatus 120-1 receives a signal via at least oneantenna, and estimates a channel characteristic for each antenna group(or data stream group) through channel estimation on the receivedsignal. The reception apparatus 120-1 acquires Channel QualityInformation (CQI) for each antenna group based on the estimated channelcharacteristic. The CQI is a value based on which channel qualitybetween each antenna group and each reception antenna can be estimated.

In addition, the reception apparatus 120-1 generates feedbackinformation based on channel quality information associated with eachantenna group. The feedback information includes a maximum CQI, anantenna group index associated with the maximum CQI, rank information,and a Remain CQI associated with the rank information. The rankinformation is a value designating the number of antenna groups viawhich the reception apparatus 120-1 will transmit a data stream to oneuser in the SU mode. If the rank information is ‘1’, it indicates arequest for transmission of a data stream for one user via one antennagroup. If the rank information is ‘2’, it indicates a request fortransmission of a data stream for one user via two antenna groups.

The transmission apparatus 110 determines a transmission mode dependingon feedback information provided from each of the reception apparatuses120-1 and 120-N. That is, the transmission apparatus 110 can selectivelyuse the SU mode and the MU mode.

To this end, the reception apparatus 120-1 includes at least onereception antenna Ant_rx #1, Ant_rx #2, . . . , Ant_rx #N_(r), a channelestimator 122-1, and a feedback information generator 124-1. Thetransmission apparatus 110 includes multiple transmission antennas(Ant_tx #1, Ant_tx #2, . . . , Ant_tx #N_(t)), a feedback informationprocessor 114, and a data transmitter 112.

Regarding the reception apparatus 120-1, a signal received from at leastone reception antenna Ant_rx #1, Ant_rx #2, . . . , Ant_rx #N_(r) isinput to the channel estimator 122-1. The channel estimator 122-1estimates a channel characteristic for each of all channels (i.e. datastream groups or antenna groups) over which the signal is transmitted.In addition, based on the estimated channel characteristic, the channelestimator 122-1 calculates CQI information associated with each of thedata stream groups transmitted via each antenna group by means of apredetermined signal detection technique.

The signal detection technique is classified into a linear detectiontechnique and a nonlinear detection technique. A Minimum Mean SquareError (MMSE) technique can be a typical example of the linear detectiontechnique, and an SIC technique can be a typical example of thenonlinear detection technique. An exemplary embodiment of the presentinvention will be described with reference to the MMSE technique, theSIC technique, and a beam-forming technique.

The channel estimator 122-1 can selectively use the MMSE technique, theSIC technique, and the beam-forming technique. The channel estimator122-1 provides CQI information of each antenna group estimated by theMMSE technique, CQI information of each antenna group measured by theSIC technique, and CQI information of each antenna group measured by thebeam-forming technique, to the feedback information generator 124-1.

The feedback information generator 124-1 generates feedback informationdepending on the CQI information for each antenna group provided fromthe channel estimator 122-1. The function of the channel estimator 122-1for acquiring CQI information by means of the various signal detectiontechniques can also be implemented to be performed in the feedbackinformation generator 124-1.

The feedback information, as stated above, includes a maximum CQI,antenna group index associated with the maximum CQI, rank information,and a Remain CQI associated with the rank information. The maximum CQIis the best CQI among the CQIs acquired for each antenna group. The rankinformation corresponds to the number of antenna groups. For example, ifthe number of antenna groups is assumed to be 2, the rank informationcan be ‘1’ or ‘2’. The Remain CQI can be differently defined accordingto the rank information. For example, if the rank information is ‘1’,the Remain CQI is CQI that can be obtained for the remaining data streamgroup after turning off an antenna group (or data stream group) havingthe minimum CQI by means of the beam-forming technique. If the rankinformation is ‘2’, the Remain CQI is CQI that can be obtained for theremaining antenna group (or data stream group) after removing themaximum CQI by means of the SIC technique.

The reception apparatus 120-1 transmits the feedback informationgenerated by the feedback information generator 124-1 to thetransmission apparatus 110. Preferably, the transmission of the feedbackinformation is periodically performed by the reception apparatus 120-1.However, if the transmission time is previously agreed upon between thetransmission apparatus 110 and the reception apparatus 120-1, thefeedback information can be aperiodically transmitted.

Regarding the transmission apparatus 110, the feedback informationreceived from all the reception apparatuses 120-1 and 120-N is providedto the feedback information processor 114. The feedback informationprocessor 114 determines a transmission mode, a coding technique, and anMCS level based on the feedback information received from each receptionapparatus.

The feedback information processor 114 calculates a sum rate (R_MU) inthe MU mode and a sum rate (R_SU) in the SU mode to determine thetransmission mode. The calculation of the R_MU and the R_SU is madedepending on the feedback information. In addition, the feedbackinformation processor 114 determines a coding technique and an MCS levelfor supporting the determined transmission mode.

The data transmitter 112 transmits, via an antenna group, at least oneuser data stream selected depending on the transmission mode, the codingtechnique, and the MCS level provided by the feedback informationprocessor 114.

B. Structure and Operation of Reception Apparatus

FIG. 2 illustrates an example of a detailed structure of a receptionapparatus according to an exemplary embodiment of the present invention.It is assumed in FIG. 2 that two data stream groups are transmitted,that is data streams are transmitted from a transmission apparatus viatwo antenna groups.

Referring to FIG. 2, a signal received via N_(R) antennas is provided toa channel estimator & feedback information generator 210 and a groupsignal detector 220.

The group signal detector 220 detects multiple data streams from thereceived signal by applying a predetermined signal detection technique.The predetermined signal detection technique can be any one of anonlinear signal detection technique and a linear signal detectiontechnique. The SIC technique can be applied as an example of thepredetermined signal detection technique. The multiple data streams,data streams transmitted via an antenna group of a transmitting entity(or the transmission apparatus), are classified into two data streamgroups. However, when the data streams are transmitted by thetransmitting entity by means of the beam-forming technique, the multipledata streams can be classified into one data stream group. Thebeam-forming technique corresponds to a signal transmission techniquefor transmitting data streams via one antenna group in a concentratedmanner.

The multiple data streams detected by the group signal detector 220 areprovided to a spatial demultiplexing block 230. The spatialdemultiplexing block 230 demultiplexes the multiple data streamsseparately for each data stream group, and outputs a data streamassociated with each data stream group.

To this end, the spatial demultiplexing block 230 can be composed of aspatial demultiplexer associated with each antenna group (i.e. each datastream group). In FIG. 2, because the number of antenna groups isassumed to be 2, the spatial demultiplexing block 230 is composed of twospatial demultiplexers 232 and 234. Therefore, the spatialdemultiplexers 232 and 234 each demultiplex the multiple data streamsprovided from the group signal detector 220, and output one data streamcorresponding to a unique data stream group.

The data stream of each data stream group, output from the spatialdemultiplexing block 230, is provided to a demodulation block 240. Thedemodulation block 240 performs demodulation on the data stream providedseparately for each data stream group.

The demodulation block 240 is composed of multiple demappers 242 and 244associated with each data stream group. The multiple demappers 242 and244 each perform demodulation, that is demapping, on the data streamsprovided from their associated spatial demultiplexers 232 and 234, andoutput demodulated data streams.

The demodulated multiple data streams output from the demodulation block240 are provided to a decoding block 250. The decoding block 250performs decoding on the demodulated data streams for each data streamgroup by means of a predetermined decoding technique. A turbo decodingtechnique can be used as an example of the predetermined decodingtechnique.

The decoding block 250 is composed of multiple decoders 252 and 254associated with each data stream group. The multiple decoders 252 and254 each perform decoding on the demodulated data streams provided fromtheir associated demappers 242 and 244.

The channel estimator & feedback information generator 210 estimates achannel characteristic associated with each data stream group by channelestimation on the received signal provided via the N_(R) antennas. Inaddition, the channel estimator & feedback information generator 210acquires CQI associated with each data stream group based on the channelcharacteristic estimated separately for each data stream group. The CQIcan be represented by an Effective Signal-to-Noise Ratio (ESN). In thefollowing description, the CQI and the ESN will be used together.Nevertheless, application of an exemplary embodiment of the presentinvention shall not be limited to the CQI or ESN. Meanwhile, varioussignal detection techniques can be used to acquire an ESN from thechannel characteristic. An exemplary embodiment of the present inventionuses the MMSE technique, the SIC technique, and the beam-formingtechnique.

In addition, the channel estimator & feedback information generator 210generates feedback information based on the ESN (where j is a datastream group index or an antenna group index) acquired separately foreach data stream group. The feedback information includes a maximum ESN(MAX-ESN), an antenna group index (MAX group index) associated with theMAX-ESN, rank information (RANK), and a Remain ESN (Remain-ESN)associated with the rank information. The MAX-ESN is the best ESN amongthe ESNs acquired separately for each data stream group, and the MAXgroup index is an antenna group index (i.e. data stream group index) ofthe MAX-ESN. In addition, the rank information, indicative of the numberof data streams (i.e. the number of data stream groups) transmitted bythe transmitting entity via an antenna group, is information used fordetermining a transmission mode of the transmitting entity. TheRemain-ESN can be acquired by means of a signal detection techniquedesignated individually for each rank information.

For example, the channel estimator & feedback information generator 210estimates an ESN associated with each data stream group by applyingthree different signal detection techniques. That is, the channelestimator & feedback information generator 210 acquires a MAX-ESN and aMAX group index depending on the best MMSE-ESN_(m) _(—) _(best) amongthe ESNs (MMSE-ESNs) estimated by means of a first signal detectiontechnique among the three signal detection techniques. The MMSEtechnique can be used as the first signal detection technique, which isa linear detection technique.

Further, the channel estimator & feedback information generator 210acquires an ESN_(n) (SIC-ESN_(n), where n is different from m_best)associated with a particular data stream group by means of a secondsignal detection technique available for rank information=‘2’ among thethree signal detection techniques. The SIC technique can be used as thesecond signal detection technique, which is a nonlinear detectiontechnique.

In addition, the channel estimator & feedback information generator 210acquires an ESN_(n) (OFF-ESN_(n), where n is different from m_best)associated with a particular data stream group by means of a thirdsignal detection technique (for example, the beam-forming technique)available for rank information=‘1’ among the three signal detectiontechniques. The beam-forming technique can be used as the third signaldetection technique. The beam-forming technique turns off the remainingantenna groups except for one antenna group among the antenna groups,and performs channel estimation only on the data stream transmitted viathe one non-turned-off antenna group. The turned-off data stream groupcorresponds to the data stream group having the minimum channel quality.

Further, the channel estimator & feedback information generator 210determines one of the SIC-ESN_(n) and the OFF-ESN_(n) as a Remain-ESN.For example, the channel estimator & feedback information generator 210determines, as a Remain-ESN, an ESN capable of obtaining a higher rateamong a rate (R_(SIC)) calculated depending on the SIC-ESN_(n) and arate (R_(OFF)) calculated depending on the OFF-ESN_(n). The channelestimator & feedback information generator 210 further considers theMAX-ESN for calculation of the R_(SIC). The channel estimator & feedbackinformation generator 210 determines, as rank information, a rank valueassociated with the signal detection technique used for acquiring theESN determined as the Remain-ESN.

A detailed description of an operation of the channel estimator &feedback information generator 210 for acquiring the feedbackinformation will be made in the description of an operation of thereception apparatus. Although the structure for channel estimation andthe structure for generating feedback information are united in a singlestructure in FIG. 2, they can be implemented with separate structures.

FIG. 3 illustrates an exemplary operation of a reception apparatus forgenerating feedback information according to an embodiment of thepresent invention. The operation shown in FIG. 3 can be performed by achannel estimator & feedback information generator in the receptionapparatus.

Referring to FIG. 3, in step 310, a reception apparatus estimates achannel characteristic H associated with each antenna included in atransmitting entity from a signal received via antennas. That is, if thenumber of antennas in the transmitting entity is assumed to be N_(T),the channel characteristic H can be defined as [h₁, h₂, . . . , h_(NT)].

In step 312, the reception apparatus calculates an MMSE-ESN_(J) of eachantenna group by means of the MMSE technique based on the estimatedchannel characteristic H. In step 314, the reception apparatus selects,as a MAX-ESN, the best MMSE-ESN from among the MMSE-ESN calculated foreach antenna group, and selects, as a MAX group index, an antenna groupindex associated with the selected MAX-ESN.

Thereafter, in step 316, the reception apparatus calculates an SIC-ESNand an OFF-ESN. That is, the reception apparatus calculates the SIC-ESNby means of the SIC technique based on the estimated channelcharacteristic H. In addition, the reception apparatus calculates theOFF-ESN by means of the beam-forming technique based on the estimatedchannel characteristic H. The SIC-ESN is calculated for one of theantenna groups, and the antenna group index associated with the SIC-ESNis different from the MAX group index. The OFF-ESN is calculated for oneof the antenna groups, and the antenna group index associated with theOFF-ESN is different from the antenna group index associated with theSIC-ESN.

In step 318, the reception apparatus calculates a rate R_(SIC) that itcan obtain when applying the SIC technique, and a rate R_(OFF) that itcan obtain when applying the beam-forming technique. For the calculationof the R_(SIC), the MAX-ESN and the SIC-ESN are used, and for thecalculation of the R_(OFF), the OFF-ESN is used.

In step 320, the reception apparatus determines a RANK and a Remain-ESN,each corresponding to the feedback information. For the Remain-ESN, thereception apparatus compares the R_(SIC) with the R_(OFF), and selects ahigher one of them. Further, the reception apparatus checks a signaldetection technique associated with the selected rate, and determines,as a Remain-ESN, the ESN calculated for the checked signal detectiontechnique. The RANK is determined according to the determinedRemain-ESN. The RANK is previously designated for the signal detectiontechnique.

For example, if the R_(SIC) is higher than the R_(OFF), the receptionapparatus determines the SIC-ESN as a Remain-ESN, and determines ‘2’associated with the SIC technique as a RANK value. However, if R_(OFF)is higher than the R_(SIC), the reception apparatus determines theOFF-ESN as a Remain-ESN, and determines ‘1’ associated with thebeam-forming technique as a RANK value.

In step 322, the reception apparatus generates feedback information. Thefeedback information includes the MAX-ESN and the MAX group indexdetermined in step 314, and the RANK and the Remain-ESN determined instep 320. Further, the reception apparatus transmits the feedbackinformation to the transmission apparatus.

FIG. 4 illustrates an operation performed in a reception apparatus with,for example, two antenna groups according to an exemplary embodiment ofthe present invention.

Referring to FIG. 4, in step 410, a reception apparatus estimates achannel characteristic H associated with each antenna included in atransmitting entity from a signal received via antennas. That is, if thenumber of antennas in the transmitting entity is assumed to be N_(T),the channel characteristic H can be defined as [h₁, h₂, . . . , h_(NT)].

In step 412, the reception apparatus calculates an MMSE-ESN₁ and anMMSE-ESN₂ by means of the MMSE technique based on the estimated channelcharacteristic H. The MMSE-ESN₁ associated with a first antenna groupcan be calculated by Equation (1), and the MMSE-ESN₂ associated with asecond antenna group can be calculated by Equation (2).

$\begin{matrix}{{f_{r}\left( {\rho_{g},1} \right)} = {\sum\limits_{m = 1}^{N_{T}/2}{f_{r}\left( \rho_{m} \right)}}} & (1) \\{{f_{r}\left( {\rho_{g},2} \right)} = {\sum\limits_{m = {{({N_{T}/2})} + 1}}^{N_{T}}{f_{r}\left( \rho_{m} \right)}}} & (2)\end{matrix}$

Herein, ρ_(m) denotes a CQI estimated for an m^(th) transmissionantenna, and a capacity function can be defined as ƒ_(r)(ρ)=log₂(1+Γρ),where Γ denotes a performance difference between the actual processingperformance and the Shannon capacity.

As defined in Equation (1) and Equation (2), the CQI associated witheach antenna group is calculated by a sum of CQIs of the individualantennas constituting each antenna group.

The ρ_(m) by the MMSE technique is calculated by Equation (3).

$\begin{matrix}{\rho_{m} = {{h_{m}^{H}\left( {{\sum\limits_{l \neq m}{h_{l}h_{l}^{H}}} + {\frac{4}{S\; N\; R}I}} \right)}h_{m}}} & (3)\end{matrix}$

In step 414, the reception apparatus decides a better MMSE-ESN fromamong the MMSE-ESN₁ and the MMSE-ESN₂. That is, the reception apparatusdetermines whether the MMSE-ESN₁ is greater than the MMSE-ESN₂. If theMMSE-ESN₁ is greater than the MMSE-ESN₂, the reception apparatusproceeds to step 416.

In step 416, the reception apparatus sets the MAX group index to ‘1’indicating the first antenna group, and sets the MAX-ESN to MMSE-ESN₁.

In the above-described manner, the reception apparatus calculates anMMSE-ESN in association with each antenna group and a mappingrelationship between the MAX-ESN set by the calculated MMSE-ESN. The MAXgroup index is shown in Table 1.

TABLE 1 antenna group index calculated ESN Group 1 MMSE-ESN₁ Group 2MMSE-ESN₂ MAX-ESN MMSE-ESN₁ MAX group index 1

In step 418, the reception apparatus calculates an SIC-ESN₂ and anOFF-ESN₁, and sets them to SIC-ESN and OFF-ESN, respectively. Tocalculate SIC-ESN, the reception apparatus should first detect the datastream transmitted by the first antenna group (an antenna groupcorresponding to the MAX group index). The reason is because MMSE-ESN₁is set to MAX-ESN. In addition, the reception apparatus acquires an ESN(SIC-ESN₂) associated with the data stream transmitted by the secondantenna group from the received signal from which the data streamcomponent transmitted by the first antenna group is removed. To acquirethe OFF-ESN₁, the reception apparatus turns off the antennas belongingto the second antenna group, and acquires an ESN (OFF-ESN₁) associatedwith the data stream transmitted by the first antenna group.

However, if MMSE-ESN₂ is greater than the MMSE-ESN₁ in step 414, thereception apparatus proceeds to step 420. It is provided in FIG. 4 thatif the MMSE-ESN₁ is equal to the MMSE-ESN₂, the reception apparatusproceeds to step 420. Alternatively, however, if the MMSE-ESN₁ is equalto the MMSE-ESN₂, the reception apparatus can be implemented to proceedto step 416.

In step 420, the reception apparatus sets the MAX group index to ‘2’indicating the second antenna group, and sets the MAX-ESN to MMSE-ESN₂.

In the above-described manner, the reception apparatus calculates anMMSE-ESN in association with each antenna group and a mappingrelationship between the MAX-ESN set by the calculated MMSE-ESN. The MAXgroup index is shown in Table 2.

TABLE 2 antenna group index calculated ESN Group 1 MMSE-ESN₁ Group 2MMSE-ESN₂ MAX-ESN MMSE-ESN₂ MAX group index 2

In step 422, the reception apparatus calculates an SIC-ESN₁ and anOFF-ESN₂, and sets them to SIC-ESN and OFF-ESN, respectively. Tocalculate the SIC-ESN, the reception apparatus should first detect thedata stream transmitted by the second antenna group (an antenna groupcorresponding to the MAX group index). The reason is because theMMSE-ESN₂ is set to MAX-ESN. Further, the reception apparatus acquiresan ESN (SIC-ESN₁) associated with the data stream transmitted by thefirst antenna group from the received signal from which the data streamcomponent transmitted by the second antenna group is removed. To acquirethe OFF-ESN₂, the reception apparatus turns off the antennas belongingto the first antenna group, and acquires an ESN (OFF-ESN₂) associatedwith the data stream transmitted by the second antenna group.

A further detailed description will now be made of an operation ofcalculating the SIC-ESN and the OFF-ESN.

The reception apparatus calculates the SIC-ESN assuming that the rank is2, and calculates the OFF-ESN assuming that the rank is 1. On thisconsumption, the SIC-ESN and the OFF-ESN can be calculated by Equation(4).

$\begin{matrix}{\rho_{g,\min}^{Remain} = \left\{ \begin{matrix}{\rho_{g,I_{g,\min}}^{BF},} & {{{if}\mspace{14mu} r} = 1} \\{\rho_{g,I_{g,\max}}^{SIC},} & {{{if}\mspace{14mu} r} = 2}\end{matrix} \right.} & (4)\end{matrix}$

where I=_(g,min)=arg min{ρ_(g,1),ρ_(g,2)}, and ρ_(g,min) ^(Remain)denotes a Remain-ESN.

The ρ_(g,m) ^(BF) calculated by Equation (4) is an SINR received bymeans of the beam-forming (BF) technique, and can be expressed asEquation (5) for m=1 and 2.

$\begin{matrix}{{f_{r}\left( \rho_{g,m}^{BF} \right)} = {\sum\limits_{l = {{2m} - 1}}^{2m}{f_{r}\left( \rho_{l}^{BF} \right)}}} & (5)\end{matrix}$

where ρ_(m) ^(BF) denotes a CQI of an m^(th) transmission antenna towhich beam-forming is applied.

The ρ_(m) ^(BF) is calculated by Equation (6).

$\begin{matrix}{\rho_{m}^{BF} = {{h_{m}^{H}\left( {{\sum\limits_{{l \neq m},{l \in A_{l}}}^{\;}{h_{l}h_{l}^{H}}} + {\frac{2}{S\; N\; R}I}} \right)}h_{m}}} & (6)\end{matrix}$

where

$A_{l} = {\left\{ {{{2\left\lbrack \frac{l + 1}{2} \right\rbrack} - 1},{2\left\lbrack \frac{l + 1}{2} \right\rbrack}} \right\}.}$

In addition, the ρ_(g,m) ^(SIC) in Equation (4) is an SINR received bymeans of the SIC technique, can be expressed as Equation (7) for m=1 and2.

$\begin{matrix}{{f_{t}\left( \rho_{g,m}^{GSIC} \right)} = {\sum\limits_{l = {{2m} - 1}}^{2m}{f_{r}\left( \rho_{l}^{GSIC} \right)}}} & (7)\end{matrix}$

where ρ_(m) ^(GSIC) denotes a CQI calculated for an m^(th) antenna groupafter removing the signal transmitted by the remaining antenna groupexcept for the m^(th) antenna group.

The ρ_(m) ^(GSIC) is calculated by Equation (8).

$\begin{matrix}{\rho_{m}^{GSIC} = {{h_{m}^{H}\left( {{\sum\limits_{{l \neq m},{l \in A_{i}}}{h_{l}h_{l}^{H}}} + {\frac{4}{S\; N\; R}I}} \right)}h_{m}}} & (8)\end{matrix}$

After acquiring the SIC-ESN and the OFF-ESN in step 418 and/or step 422,the reception apparatus proceeds to step 424 where it calculates a rateR_(SIC) that it can obtain when applying the SIC technique, and a rateR_(OFF) that it can obtain when applying the beam-forming technique. TheR_(SIC) and the R_(OFF) can be calculated by Equation (9).

R _(BF)=ƒ_(r)(ρ_(g,I) _(g,max) ^(BF))

R _(GSIC)=ƒ_(r)(ρ_(g,I) _(g,max) )+ƒ_(r)(ρ_(g,I) _(g,min) ^(GSIC))  (9)

In step 426, the reception apparatus determines whether the R_(OFF) ishigher than the R_(SIC). If the R_(OFF) is higher than the R_(SIC), itmeans that transmitting the data stream by means of the beam-formingtechnique is superior in terms of the transmission efficiency.Otherwise, if the R_(SIC) is higher than the R_(OFF), transmitting thedata stream by means of the SIC technique is superior in terms of thetransmission efficiency.

If the R_(OFF) is higher than the R_(SIC), the reception apparatusproceeds to step 428. However, if the R_(SIC) is higher than theR_(OFF), the reception apparatus proceeds to step 430. It is provided inFIG. 4 that if the R_(OFF) is equal to the R_(SIC), the receptionapparatus proceeds to step 430. Alternatively, however, if the R_(OFF)is equal to the R_(SIC), the reception apparatus can be implemented toproceed to step 428.

In step 429, the reception apparatus sets the rank information to avalue ‘1’ corresponding to the use of the beam-forming technique, andsets the Remain-ESN to the calculated OFF-ESN. Otherwise, in step 430,the reception apparatus sets the rank information to a value ‘2’corresponding to the use of the SIC technique, and sets the Remain-ESNto the calculated SIC-ESN.

In the above-described manner, the reception apparatus acquires theMAX-ESN, the MAX group index, the RANK, and the Remain-ESN, generatesfeedback information depending on the acquired MAX-ESN, MAX group index,RANK and Remain-ESN, and transmits the feedback information to thetransmission apparatus.

C. Structure and Operation of Transmission Apparatus

FIG. 5 illustrates an example of a detailed structure of a transmissionapparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 5, a feedback information processor 510 receivesfeedback information from all reception apparatuses and controls theoverall operation of transmitting data streams depending on the feedbackinformation.

More specifically, the feedback information processor 510 determines atransmission mode, a coding technique, and an MCS level based on thefeedback information received from each reception apparatus. Thetransmission mode is classified into the SU mode and the MU mode.

The feedback information processor 510 calculates an R_MU and an R_SU todetermine the transmission mode. The feedback information processor 510calculates the R_MU depending on a MAX-ESN and a MAX group index in thereceived feedback information. The feedback information processor 510calculates the R_SU depending on a RANK, a Remain-ESN, and a MAX-ESN inthe received feedback information.

For example, to calculate the R_MU, the feedback information processor510 should collect a MAX-ESN individually for each antenna groupdepending on the MAX group index. Further, the feedback informationprocessor 510 selects a best CQI (MAX-ESN_(i,j), where i denotes a userindex and j denotes a antenna group index) individually for each antennagroup from among the MAX-ESNs collected in association with each antennagroup, and calculates the R_MU by the sum of MAX-ESN_(i,j) selectedindividually for each antenna group.

To calculate the R_SU, the feedback information processor 510 shouldcollect a CQI (MAX-ESN or Remain-ESN) associated with each antenna grouptaking RANK into account. Further, the feedback information processor510 calculates a sum rate (R_SU_i, where i denotes a user index)individually for each transmission apparatus based on the CQI collectedin association with each antenna group, and calculates the best rateamong the R_SU_i as the R_SU.

Thereafter, the feedback information processor 510 compares the R_MUwith the R_SU, and selects one of the MU mode and the SU mode as atransmission mode according to the comparison result. For example, ifthe R_SU is equal to or less than the R_RU, the feedback informationprocessor 510 selects the MU mode as a transmission mode. However, ifthe R_SU is greater than the R_MU, the feedback information processor510 selects the SU mode as a transmission mode.

In addition, the feedback information processor 510 determines an MCSlevel and user scheduling information for supporting the SU mode and/orthe MU mode. The user scheduling information is control information usedfor selecting a user data stream that the transmission apparatus willtransmit according to the transmission mode.

A user stream processor 520 receives data associated with each ofmultiple users User #1 to User #K, groups the data of each user underthe control of the feedback information processor 510, and outputs thegrouped data as at least one data stream. The user stream processor 520selects the received user data depending on the transmission mode andthe user scheduling information provided from the feedback informationprocessor 510 and outputs the selected data as at least one data stream.If the MU mode is designated, the user stream processor 520 outputs asmany user data streams as the number of antenna groups. However, if theSU mode is designated, the user stream processor 520 outputs theselected user data as one data stream.

An encoding block 530 includes as many encoders as the number of antennagroups. In FIG. 5, as the number of antenna groups is assumed to be two,the encoding block 530 is composed to two encoders 532 and 534. Theencoding block 530 performs encoding on the at least one data streamprovided from the user stream processor 520. In this case, the encodingblock 530 takes into account the MCS level provided from the feedbackinformation processor 510. That is, a coding rate in the encoding block530 is determined depending on the MCS level.

A modulation block 540 modulates the at least one data stream encoded bythe encoding block 530 taking the MCS level into consideration. Themodulation block 540 is composed of as many mappers as the number ofantenna groups. In FIG. 5, as the number of antenna groups is assumed tobe two, the modulation block 540 is composed to two mappers 542 and 544.

A spatial multiplexing block 550 is composed of spatial multiplexers 552and 554 associated with their corresponding antenna groups. The spatialmultiplexers 552 and 554 multiplex the modulated data streams providedfrom the modulation block 540 in association with their antenna groups.The number of data streams output from each of the spatial multiplexers552 and 554 corresponds to the number of antennas constituting eachantenna group. The data streams output from the spatial multiplexers 552and 554 are each transmitted via their associated antennas.

Although the feedback information processor 510 and the user streamprocessor 520 are implemented with separate structures in FIG. 5 by wayof example, it is also possible to implement to process the operation ofthe feedback information processor 510 and the operation of the userstream processor 520 by means of a single structure.

FIG. 6 illustrates a control flow performed in a transmission apparatusaccording to an exemplary embodiment of the present invention.

Referring to FIG. 6, in step 610, a transmission apparatus receivesfeedback information transmitted separately for each user. The feedbackinformation includes MAX-ESN_(i), MAX group index_(i), RANK_(i), andRemain-ESN_(i). Table 3 shows an example of feedback information thatthe transmission apparatus has received separately for each user. InTable 3, the number of users is assumed to be three, and the number ofantenna groups is assumed to be two.

TABLE 3 MAX group MAX-ESN_(i) index_(i) RANK_(i) Remain-ESN_(i) USER 1MAX-ESN₁ 2 1 Remain-ESN₁ USER 2 MAX-ESN₂ 1 2 Remain-ESN₂ USER 3 MAX-ESN₃2 1 Remain-ESN₃

In step 612, the transmission apparatus collects a MAX-ESN_(i) using aMAX group index_(i) based on the feedback information received from eachuser. That is, the transmission apparatus collects the MAX-ESN_(i)separately for each user (or reception apparatus) taking the MAX groupindex_(i) into account.

Table 4 shows an example of MAX-ESN_(i,j) collected by the transmissionapparatus that has received the feedback information shown in Table 3.

TABLE 4 USER 1 USER 2 USER 3 GROUP 1 — MAX-ESN_(2,1) — GROUP 2MAX-ESN_(1,2) — MAX-ESN_(3,2) m_best 2 1 2

As can be appreciated from Table 4, the transmission apparatus checksMAX-ESN_(i) and MAX group index_(i) individually for each user, and mapsthe checked MAX-ESN_(i) to the antenna group designated by the MAX groupindex_(i). The MAX-ESN_(i) mapped in this rule is expressed asMAX-ESN_(i,j) taking the antenna group index into consideration, where jdenotes an antenna group index. Further, in Table 4, m_best correspondsto the MAX group index checked separately for each user.

For example, MAX-ESN₁ received from USER 1 is mapped to MAX-ESN_(1,2)because its MAX group index is ‘2’, and MAX-ESN₂ received from USER 2 ismapped to MAX-ESN_(2,1) because its MAX group index is ‘1’.

In step 614, the transmission apparatus calculates an R_MU depending onthe collected information. To this end, the transmission apparatusselects the best MAX-ESN_(i,j) from among MAX-ESN_(i,j) collectedseparately for each antenna group, and calculates a serviceable ratedepending on the MAX-ESN_(i,j) selected individually for each antennagroup. The transmission apparatus sets the calculated rate as R_MU.

Table 5 shows an example of R_MU calculated based on the MAX-ESN_(i,j)collected as shown in Table 4.

TABLE 5 USER 1 USER 2 USER 3 Maximum GROUP 1 — MAX- — MAX-ESN_(2,1)ESN_(2,1) GROUP 2 MAX-ESN_(1,2) — MAX-ESN_(3,2) MAX-ESN_(1,2) M_best 2 12 R_MU

According to Table 5, MAX-ESN_(2,1) is selected for the first antennagroup, and MAX-ESN_(1,2) is selected for the second antenna group. Thereason why the MAX-ESN_(1,2) is selected is because the MAX-ESN_(1,2)has higher quality than the MAX-ESN_(3,2). In addition, the transmissionapparatus sets, as R_MU, the rate supportable by the MAX-ESN_(2,1)selected for the first antenna group and the MAX-ESN_(1,2) selected forthe second antenna group.

In step 616, the transmission apparatus collects MAX-ESN_(i) andRemain-ESN_(i) using RANK_(i) based on the feedback information receivedfrom each user. That is, the transmission apparatus collects theMAX-ESN_(i) and Remain-ESN_(i) separately for each antenna group takingthe RANK_(i) into account.

Table 6 shows an example of MAX-ESN_(i,j) and Remain-ESN_(i) collectedbased on the RANK_(i) by the transmission apparatus that has receivedthe feedback information shown in Table 3.

TABLE 6 USER 1 USER 2 USER 3 (RANK = 1) (RANK = 2) (RANK = 1) GROUP 1OFF MAX-ESN_(2,1) Remain-ESN_(3,1) GROUP 2 Remain-ESN_(1,2)Remain-ESN_(2,2) OFF

As can be appreciated from Table 6, the transmission apparatus collectsonly the Remain-ESN_(i) for the user with RANK_(i)=1, and collectsMAX-ESN_(i,j) and Remain-ESN_(i) for the user with RANK_(i)=2. This isbecause the SU mode by the beam-forming technique is requested for theRANK_(i)=1, and the MU mode by the SIC technique is requested for theRANK_(i)=2. Therefore, the transmission apparatus collectsRemain-ESN_(i) associated with one of two antenna groups for the USER 1with RANK_(i)=1 and the USER 3 with RANK_(i)=1. Further, thetransmission apparatus turns off the remaining antenna group. That is,for USER 1, the transmission apparatus collects Remain-ESN_(1,2) inassociation with the second antenna group and turns off the firstantenna group. For USER 3, the transmission apparatus collectsRemain-ESN_(3,1) in association with the first antenna group and turnsoff the second antenna group.

However, for USER 2 with RANK_(i)=2, the transmission apparatus collectsMAX-ESN_(i,j) for one of the two antenna groups and collectsRemain-ESN_(i,j) for the remaining antenna group. That is, for USER 2,the transmission apparatus collects MAX-ESN_(2,1) for the first antennagroup and collects Remain-ESN_(2,2) for the second antenna group.

Thereafter, in step 618, the transmission apparatus calculates an R_SUdepending on the collected information. To this end, the transmissionapparatus calculates a serviceable rate R_SU_i depending on theRemain-ESN_(i,j) or MAX-ESN_(i,j) and Remain-ESN_(i,j) collectedseparately for each user.

Table 7 shows an example of serviceable rates R_SU_1, R_SU_2, and R_SU_3calculated separately for each user based on the collected informationshown in Table 6.

TABLE 7 USER 1 USER 2 USER 3 (RANK = 1) (RANK = 2) (RANK = 1) GROUP 1OFF MAX-ESN_(2,1) Remain-ESN_(3,1) GROUP 2 Remain-ESN_(1,2)Remain-ESN_(2,2) OFF SUM RATE R_SU_1 R_SU_2 R_SU_3

The transmission apparatus compares the rates R_SU_1, R_SU_2, and R_SU_3calculated individually for each user, and selects the highest one ofthem. Further, the transmission apparatus sets the selected rate asR_SU.

Table 8 shows an example of setting R_MU on the assumption that amongthe rates R_SU_1, R_SU_2, and R_SU_3 calculated separately for each useras shown in Table 7, R_SU_3 is the highest rate.

TABLE 8 USER 1 USER 2 USER 3 (RANK = 1) (RANK = 2) (RANK = 1) MaximumGROUP 1 OFF MAX-ESN_(2,1) Remain-ESN_(3,1) Remain- ESN_(3,1) GROUP 2Remain-ESN_(1,2) Remain-ESN_(2,2) OFF OFF SUM R_SU_1 R_SU_2 R_SU_3 R_SU= RATE R_SU_3

In step 620, the transmission apparatus compares the R_MU with the R_SUto determine a supportable transmission mode. That is, the transmissionapparatus compares the R_MU with the R_SU and determines a higher rateas a supportable transmission mode.

If the R_SU is higher than the R_MU, the transmission apparatustransmits a data stream of the corresponding user by means of the SUmode in step 622. That is, the transmission apparatus transmits the datastream of the corresponding user via an antenna group associated withthe rate set as the R_SU among the multiple antenna groups. Here, thenumber of antenna groups via which the data stream of the user will betransmitted is determined according to RANK designated by thecorresponding user. For example, if RANK is designated as ‘1’, thetransmission apparatus transmits the data stream of the correspondinguser via one antenna group. In this case, the antennas corresponding tothe remaining one antenna group are turned off. However, if RANK isdesignated as ‘2’, the transmission apparatus transmits the data streamof the corresponding user via two antenna groups. According to Table 8,the transmission apparatus transmits data streams of USER 3 via thefirst antenna group at the rate R_SU_3.

Otherwise, if the R_MU is higher than the R_SU, the transmissionapparatus transmits data streams of the users selected for each antennagroup by means of the MU mode in step 624. That is, the transmissionapparatus transmits the data streams of the corresponding users via anassociated antenna group among the multiple antenna groups. The rateused at this time is a rate capable of supporting MAX-ESN_(i,j)corresponding to each user selected separately for each antenna group.According to Table 5, data streams of USER 2 are transmitted via thefirst antenna group at the rate capable of supporting MAX-ESN_(2,1), anddata streams of USER 1 are transmitted via the second antenna group atthe rate capable of supporting MAX-ESN_(1,2).

A description of the operation in which the R_SU is equal to the R_MUhas not been provided herein. It is assumed in FIG. 6 that if the R_SUis equal to the R_MU, the transmission apparatus operates in the MUmode. However, the transmission apparatus can also be implemented suchthat when the R_SU is equal to the R_MU, it operates in the SU mode.

Although an exemplary embodiment of the present invention generatesfeedback information depending on a data stream of a user and transmitsthe feedback information, by way of example, exemplary embodiments ofthe present invention can also be implemented using a signal (forexample, a pilot signal) predefined for each user instead of using thedata stream of the user. In addition, although the number of antennagroups herein is assumed to be 2, the number of antenna groups issubject to change. In this case, it is necessary to newly define RANKinformation according to the changed number of antenna group. Forexample, if an exemplary embodiment of the present invention isimplemented with three antenna groups, the RANK information should bedefined depending on the information based on which one to three antennagroups can be selected. In addition, exemplary embodiments of thepresent invention can be applied regardless of the number of users.

As is apparent from the foregoing description, according to exemplaryembodiments of the present invention, multiple receivers each extractchannel quality of an antenna group connected to a transmitter, generatefeedback information using the extracted channel quality, and thentransmit the feedback information to the transmitter, thereby reducingthe amount of feedback information compared to the case of feeding backchannel quality of each antenna.

In addition, the transmitter according to an exemplary embodiment of thepresent invention is configured to receive channel qualities fed backfrom multiple receivers, thereby enabling scheduling such that a userdata stream is transmitted individually via each antenna group. Thiscontributes to an increase in the transmission capacity of themulti-antenna system.

Further, the feedback information proposed by exemplary embodiments ofthe present invention is similar in size to the feedback informationproposed in each of the conventional SU mode and MU mode. Therefore,exemplary embodiments of the present invention can support both the SUmode and the MU mode without increasing the size of the feedbackinformation. Moreover, because the feedback information includes a rankvalue indicating the beam-forming mode and/or the SIC mode, exemplaryembodiments of the present invention can adaptively control the use ofthe feedback information when operating in the SU mode.

While the invention has been shown and described with reference to acertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

1. A method for receiving/transmitting data in a closed-loopmulti-antenna system that defines multiple antenna groups by antennagrouping on multiple antennas, and performs data transmissionindividually via each of the multiple antenna groups, the methodcomprising the steps of: receiving, by a transmitter, feedbackinformation from at least one receiver; calculating, by the transmitter,each of a sum rate (R_MU) in a multi-user mode and a sum rate (R_SU) ina single-user mode using the feedback information; selecting, by thetransmitter, one of the single-user mode and the multi-user mode as atransmission mode using a comparison result between the sum rate (R_MU)in the multi-user mode and the sum rate (R_SU) in the single-user mode;and transmitting, by the transmitter, a data stream according to theselected transmission mode, acquiring, by the at least one receiver,channel quality information (CQI) for each data stream transmittedindividually via each antenna group corresponding to the transmissionmode; determining, by the at least one receiver, CQI associatedinformation from the CQI acquired individually for each antenna group;and transmitting, by the at least one receiver, the determined CQIassociated information to the transmitter as the feedback information,wherein the CQI associated information includes maximum CQI, an antennagroup index associated with the maximum CQI, rank information, andremaining CQI associated the rank information.
 2. The method of claim 1,wherein the calculating of a sum rate (R_MU) in a multi-user modecomprises: collecting, by a transmitter, maximum CQI individually foreach antenna group using the antenna index; selecting, by a transmitter,maximum CQI individually for each antenna group from the maximum CQIcollected for each antenna group; and calculating, by a transmitter, thesum rate (R_MU) in the multi-user mode depending on a sum of the maximumCQI selected individually for each antenna group.
 3. The method of claim2, wherein the calculating of a sum rate (R_SU) in a single-user modecomprises: collecting, by a transmitter, CQI associated with eachantenna group taking into account the rank information individually forthe at least receiver; calculating, by a transmitter, a sum rateindividually for the at least one receiver using the CQI collected foreach antenna group; and determining, by a transmitter, as the sum rate(R_SU) in the single-user mode, a greatest sum rate among the sum ratescalculated individually for the at least receiver.
 4. The method ofclaim 3, wherein the CQI collected for each antenna group is one ofmaximum CQI, and remaining CQI included in feedback information receivedfrom the at least receiver.
 5. The method of claim 4, wherein theselecting of a transmission mode comprises: selecting, by a transmitter,the multi-user mode as a transmission mode if the sum rate (R_SU) in thesingle-user mode is less than or equal to the sum rate (R_MU) in themulti-user mode; and selecting, by a transmitter, the single-user modeas a transmission mode if the sum rate (R_SU) in the single-user mode isgreater than the sum rate (R_MU) in the multi-user mode.
 6. The methodof claim 1, wherein the acquiring of CQI comprises: estimating, by theat least one receiver, a channel characteristic associated with eachdata stream transmitted individually via each antenna group throughchannel estimation on the received signal; and acquiring, by the atleast one receiver, CQI associated with each data stream transmittedindividually via each antenna group using the estimated channelcharacteristic.
 7. The method of claim 6, wherein the determining ofmaximum CQI comprises: calculating, by the at least one receiver, CQIfor each data stream transmitted individually via each antenna groupusing the estimated channel characteristic using a first signaldetection technique; and comparing, by the at least one receiver, theCQI calculated individually for each data stream and determining a bestCQI as the maximum CQI.
 8. The method of claim 7, wherein thedetermining of the CQI associated information comprises: calculating, bythe at least one receiver, CQI for a data stream transmitted via one ofthe antenna groups using the estimated channel characteristic using asecond signal detection technique; calculating, by the at least onereceiver, CQI for a data stream transmitted via one of the antennagroups using the estimated channel characteristic using a third signaldetection technique; and determining, by the at least one receiver, therank information depending on the CQI calculated using the second signaldetection technique and the CQI calculated using the third signaldetection technique.
 9. The method of claim 8, wherein the first signaldetection technique is a linear detection technique, and the secondsignal detection technique is a nonlinear detection technique and thethird signal detection technique is a technique of turning off remainingantenna groups, except for one antenna group, among the antenna groups,and performing channel estimation on a data stream transmitted via theone antenna group, or the first signal detection technique is a MinimumMean Square Error (MMSE) technique, the second signal detectiontechnique is a Successive Interference Cancellation (SIC) technique, andthe third signal detection technique is a beam-forming technique. 10.The method of claim 9, wherein the determining of CQI associatedinformation comprises: calculating, by the at least one receiver, afirst rate using the maximum CQI and an Effective Signal-to-Noise Ratio(ESN) calculated by the SIC technique; calculating, by the at least onereceiver, a second rate using on an ESN calculated by the beam-formingtechnique; comparing, by the at least one receiver, the first rate withthe second rate; if the first rate is less than or equal to the secondrate, determining, by the at least one receiver, the rank information asa value for requesting transmission of multiple data streams via theantenna group, if the first rate is greater than the second rate,determining the rank information as a value for requesting transmissionof one data stream via the antenna group; and if the first rate is lessthan or equal to the second rate, determining, by the at least onereceiver, the remaining channel quality information as an ESN calculatedby the SIC technique, if the first rate is greater than the second rate,determining the remaining channel quality information as an ESNcalculated by the beam-forming technique.
 11. A closed-loopmulti-antenna system that defines multiple antenna groups by antennagrouping on multiple antennas, and performs data transmissionindividually via each of the multiple antenna groups, the closed-loopmulti-antenna system comprising: a transmitter including a feedbackinformation processor and a first transmit unit; and at least onereceiver including a channel estimator, a feedback information generatorand a second transmit unit, wherein the feedback information processorfor receiving feedback information from the at least one receiver,calculating each of a sum rate (R_MU) in a multi-user mode and a sumrate (R_SU) in a single-user mode using the feedback information, andselecting one of the single-user mode and the multi-user mode as atransmission mode depending on a comparison result between the sum rate(R_MU) in the multi-user mode and the sum rate (R_SU) in the single-usermode, the first transmit unit for transmitting a data stream accordingto the selected transmission mode, the channel estimator for acquiring,CQI for each data stream transmitted individually via each antennagroup, the feedback information generator for determining, CQIassociated information from the CQI acquired individually for eachantenna group corresponding to the transmission mode; and the secondtransmit unit for transmitting the feedback information to thetransmitter, wherein the CQI associated information includes maximumCQI, an antenna group index associated with the maximum CQI, rankinformation, and remaining CQI associated the rank information.
 12. Theclosed-loop multi-antenna system of claim 11, wherein the feedbackinformation processor collects the maximum CQI individually for eachantenna group using on the antenna index, selects maximum CQIindividually for each antenna group from the maximum CQI collected foreach antenna group, and calculates the sum rate (R_MU) in the multi-usermode depending on a sum of the maximum CQI selected individually foreach antenna group.
 13. The closed-loop multi-antenna system of claim12, wherein the feedback information processor collects CQI associatedwith each antenna group taking into account the rank informationindividually for the at least receiver, calculates a sum rateindividually for the at least one receiver using on the CQI collectedfor each antenna group, and determines, as the sum rate (R_SU) in thesingle-user mode, a greatest sum rate among the sum rates calculatedindividually for the at least receiver.
 14. The closed-loopmulti-antenna system of claim 13, wherein the CQI collected for eachantenna group is one of maximum CQI, and remaining CQI included infeedback information received from the at least receiver.
 15. Theclosed-loop multi-antenna system of claim 14, wherein the feedbackinformation processor selects the multi-user mode as a transmission modeif the sum rate (R_SU) in the single-user mode is less than or equal tothe sum rate (R_MU) in the multi-user mode, and selects the single-usermode as a transmission mode if the sum rate (R_SU) in the single-usermode is greater than the sum rate (R_MU) in the multi-user mode.
 16. Theclosed-loop multi-antenna system of claim 11, wherein the channelestimator estimates a channel characteristic associated with each datastream transmitted individually via each antenna group through channelestimation on the received signal; and acquiring CQI associated witheach data stream transmitted individually via each antenna group usingthe estimated channel characteristic.
 17. The closed-loop multi-antennasystem of claim 16, wherein the feedback information generatorcalculates CQI for each data stream transmitted individually via eachantenna group using the estimated channel characteristic using a firstsignal detection technique; and compares the CQI calculated individuallyfor each data stream and determining a best CQI as the maximum CQI. 18.The closed-loop multi-antenna system of claim 17, wherein the feedbackinformation generator calculates CQI for a data stream transmitted viaone of the antenna groups using the estimated channel characteristicusing a second signal detection technique, calculates CQI for a datastream transmitted via one of the antenna groups using the estimatedchannel characteristic using a third signal detection technique; anddetermines the rank information using the channel quality informationcalculated using the second signal detection technique and the channelquality information calculated using the third signal detectiontechnique.
 19. The closed-loop multi-antenna system of claim 18, whereinthe first signal detection technique is a linear detection technique,and the second signal detection technique is a nonlinear detectiontechnique and the third signal detection technique is a technique ofturning off remaining antenna groups, except for one antenna group,among the antenna groups, and performing channel estimation on a datastream transmitted via the one antenna group, or the first signaldetection technique is a Minimum Mean Square Error (MMSE) technique, thesecond signal detection technique is a Successive InterferenceCancellation (SIC) technique, and the third signal detection techniqueis a beam-forming technique.
 20. The closed-loop multi-antenna system ofclaim 19, wherein the feedback information generator calculates a firstrate using the maximum CQI and an Effective Signal-to-Noise Ratio (ESN)calculated by the SIC technique, calculates a second rate using on anESN calculated by the beam-forming technique, comparing the first ratewith the second rate; if the first rate is less than or equal to thesecond rate, determining the rank information as a value for requestingtransmission of multiple data streams via the antenna group, if thefirst rate is greater than the second rate, determining the rankinformation as a value for requesting transmission of one data streamvia the antenna group; and if the first rate is less than or equal tothe second rate, determining the remaining channel quality informationas an ESN calculated by the SIC technique, if the first rate is greaterthan the second rate, determining the remaining channel qualityinformation as an ESN calculated by the beam-forming technique.